Synchronous advanced argillic alteration and deformation in a shear zone-hosted magmatic hydrothermal Au-Ag deposit at the Temora (Gidginburg) Mine, New South Wales, Australia

Article type :

Economic geology & mineral exploration

Location :

proceedings of economic geology journal 1976-96

Fulltext :

Abstract: Paragenetic relations indicate that advanced argillic alteration at the Temora mine and the adjacent Dam- Lilydale prospect is coeval with movement along shear zones which host each system. The interaction between movement along the host structure and developing alteration zones of contrasting rheology controlled the flow of hydrothermal fluid and resultant overall system geometry. Neither of these systems represents older, typical epithermal or porphyry-related systems that were subsequently deformed. However, advanced argillic alteration at both prospects cuts across the peripheral parts of older porphyry-style alteration systems, with paragenetic relations analogous to the Butte and Dizon districts. Each system is characterized by an early phase of massive or breccia-textured, quartz-dominated advanced argillic alteration, cut by foliated mica-rich, quartz-absent advanced argillic alteration. Phase relations indicate that early quartz-saturated advanced argillic alteration developed at temperatures < or =275 degrees C, whereas later quartz-absent advanced argillic alteration developed at temperatures between 275 degrees and 340 degrees C. Most types of advanced argillic alteration are barren, but background 0.2 to 1 ppm Au grades are locally associated with silica-pyrite alteration. In the Temora mine, economic Au grades are associated with barite- sulfide veins that are generally confined to the silica-pyrite core of the earlier quartz-rich advanced argillic alteration. Cu-Au mineralization at the Dam prospect is associated with sericite-clay-chlorite alteration inferred to be the deeper level equivalent of quartz-absent advanced argillic alteration in the Temora mine. Ore- bearing veins in the Temora mine predate this quartz-absent alteration and were deformed and partly remobilized. The restricted distribution of ore-bearing veins in the silica-pyrite core of the Temora mine reflects the brittle rheology and susceptibility of this rock type to failure during movement along the host...